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How much force does a helicopter's tail rotor counteract?
How much force does a helicopters tail rotor counteract?
What are the formulas for determining this? How much rotational torque is produced by spinning the blades?

Multiply engine output with a efficiency factor of about 3/4 to get the power at the main rotor, divide by rpm you get the torque at the rotor, divided by the length of the tail you get the force at the tail. If you get the efficiency number right this should be pretty accurate.

@user3528438  But don't forget that only a small part of the power absorbed by the rotor is used to overcome the drag of the rotor blades, since most of that power is consumed by the lift generated... It's only the blade drag that causes the torque reaction that has to be counteracted by a tail rotor...

@xxavier there is power required to overcome induced blade drag as well.

@Koyovis You're right. The part of the power related to lift is accounted by the induced drag...

The lift-to-drag ratio of the main rotor blades is around 10, so the tail roter has to provide a force equal to one tenth of the aircraft's weight.
Of course you have to take into consideration torques and lever arms, but if we assume that most of the lift and drag is created by the outer portion of the main rotor and that the tail rotor's lever arm is approximately the same, we can simply ignore them. On most helicopters the tail boom is a bit longer than the radius of the main rotor, so the force might be 20-50% lower. On the other hand, the tail rotor is often less efficient, especially on some newer models with small, ducted fans, so the tail rotor might consume a bit more than 10% of the power.

A very clear and simple explanation, directly from first principles...

The tail rotor on helicopters indeed provides anti-torque thrust, plus thrust for manoeuvring in the yaw axis. A quote from Principles of Helicopter Aerodynamics by j. Gordon Leishman section 6.9:

The magnitude of this thrust, as well as its power consumption, depends on the reaction torque from the main rotor, $Q_{MR}$, and the location of the tail rotor from the centre of gravity (i.e. the moment arm $l_{MR}$). In addition, there are inertial effects that the tail rotor must overcome during yawing manoeuvres. In this case, the tail rotor thrust can be found from $$Q_{MR} + I_{ZZ} \ddot{\Psi} = T_{TR} \cdot l_{TR}$$ where $\ddot{\Psi}$ is the yaw acceleration and $I_{ZZ}$ is the mass moment of inertia of the helicopter about the yaw axis.

The main rotor torque $Q_{MR}$ can be computed from the installed net power and the main rotor RPM. For instance for the Bell 212, for which we have done a simulator aerodynamic model:

Installed derated TO power $P_I$= 962 kW
Rotor RPM = 320 => $\Omega$ = 33.5 rad/sec
Main rotor torque $T = P_I / \Omega  = 962 * 10^3 / 33.5$ = 28,716 Nm

With a tail rotor moment arm of 8.82m, the tail rotor thrust would then be 28,716/8.82 ≃ 3,260 N
And indeed the above method must account for power losses:

The power to drive the tail rotor is between 10-20% of the installed power and is lost completely, unless the tail rotor is canted.
Transmission between engine and rotors causes friction losses.
Installed hydraulic & electrical systems require engine power.

A complete method for computing tail rotor performance is quite broad in scope, and can be found for instance in Helicopter Performance, Stability and Control by Ray Prouty, chapter 3.

Now if we think about it this way, the tail rotor and main rotor perform very similarly (assume so for a guesstimate) and tail takes 10%-20% the power, then the force if the tail rotor would be 10%-20% of the weight of the helicopter plus some room for maneuverability.


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Why are jet engine nacelles, used on the same plane, so different?
One thing that is plainly obvious about the design and configuration of jet airliners is how little they tend to differ.
It's surprising then that even on the same airliner, you will see two quite different-looking engines.
I've seen A330s with "fully-enclosed" engines, and "open" engines:
(Trent 700 with exhaust mixer, image from Wikipedia).
(PW4000 with unmixed exhaust, image from Wikipedia).
The fact that both designs are used suggests that one isn't simply better than the other, but the difference seems fairly significant.
Why would an engine designer or a customer opt for one design over the other, and why do they arrive at such apparently different solutions for the same use-case?
I assume, perhaps incorrectly, that each has its own advantages and that for whatever reasons different manufacturers and customers value different ones.

@ymb1. The question said to be the duplicate and give the answer, really doesn't, IMHO. The first answer says it due to noise restrictions, but that makes no sense, because both engines are subject to the same noise requirements. The second answer might be in the right direction, but is very very short. So, a good answer is still lacking. What do you think? I realise you are not the only person who voted this question as a duplicate, but I can only tag 1 person. Cheers

@Penguin I have given up really trying to discuss whether questions should be closed. It seems for example that the faintest overlap of subject with another question or its answer is enough to have a question closed, no matter what the actual question is, or whether it is actually answered in any satisfactory way. Obviously I don't agree it's a duplicate, but arguing about that isn't how I wish to spend my time. Nor is there much incentive to spend energy carefully researching or composing a question if it's going to be closed at the first opportunity.

@DanieleProcida. I don't disagree with your view !

@ymb1. Thanks for reply, I have made a comment to the author. ( I thought that question / bounty had been allocated, as the question has a green tick.)

I am still hoping that I will discover one day what is being considered when engine designers and customers choose one design over another - what advantages are they trading-off, and what makes different advantages more important for different designers/customers? This is not asked, or answered, in the supposed duplicate.

@DanieleProcida Please update your question with this information you provided in the comment and then it can be reopened.

Sometimes manufacturers will certify with multiple engine types because their customers have their own power plant preferences (or manufacturer preferences, like say an airline's existing fleet is RR engines and they want to keep engine commonality for logistics benefits, or an airline feels one model engine is cheaper to run than another).  Providing different powerplant options for an airliner can therefore result in more sales.

This explains why there are different engine options, but not why different engines make different design decisions, which is what the question is asking.

In that case it would be differences in mission profile.  Generally an engine with a lower bypass ratio is better at higher altitudes, so an airline might go for that because of their mission profile has a preference for very high altitude long range performance which favours a lower bypass ratio vs another engine with a higher bypass that is optimized for climbs to 30 something thousand ft on 2 hour legs..

The bypass ratio also isn't the aspect being asked about - it's the mixed vs unmixed exhaust design.

The mixed exhaust is a sign of a lower bypass ratio, which is the most significant aspect.  Also, shrouding the core tail pipe with fan exhaust may reduce the noise level somewhat, so there's that.

Hi John. "The mixed exhaust is a sign of a lower bypass ratio". If the exhaust design was changed later in the engines life, yes, it might change the bypass ratio. But, at the time of design, why can't the designer choose the bypass ratio to be x, independently of the nozzle design? If the nozzle design affects it when a mixed nozzle is selected, he just iterates the design to get it back to the same value as it had with an unmixed nozzle. Isn't that possible? Or are you talking about the first scenario? Cheers.

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What is an autopilot washout filter?
In the context of aircraft autopilot design, I do not understand what is washout filter is [Heading Hold - Lateral Dynamics] and what is it used for.
May anyone explain to me?

If this question does not get reopen I will unsubscribe from this SE. "I don`t know therefore I downvote/flag" is really too much of a thing here :-/

As someone who's heard this term quite a few times, I can say that the closure for clarification was necessary since an autopilot might have a dozen washout filters for various functions.  However, I'm not saying that all the downvotes or closure flags here were made with that same level of justification.

@CodyP there have been no downvotes here

A washout filter is a building block of a control system.  As such, it's hard to say exactly where it'd be used, but I'll make some guesses about where it could go.  In general it's used for removing the mostly constant part of a signal or approximating a derivative.
(If you already know the basics of control systems, skip this paragraph) Control systems in general are used to connect what you can sense (gryoscope forces, IRS readings, airspeed indicators) to what the state is (attitude, position, velocity, etc.) and connect that to the desired control surface response to smoothly reach the desired attitude and velocity.  Since some of these relationships require filters like complementary filters or others are approximated by second-order differential equations, the filters used in these controls can be equally complex, incorporating elements like integrals and derivatives in their equations or even using a carefully matched second-order differential equation as the response. Imagine a designing a equation that told you what angle to hold the steering wheel based on the car's distance from the center of the lane.  That's an example of the math that would be involved here.
A washout filter simply removes any slowly-changing component of the input and preserves the fast-changing component, sometimes called "high-pass" behavior because high frequencies pass through.  This is similar to (and can even be an approximation for) taking a derivative of the input: sudden changes produce a large output, slowly changing or constant values produce almost no output.  Washout filters have a time-constant or cutoff frequency that determine where it draws the line between "fast" changes and "slow" changes.  Most washout filters are very simple (generally first order) and, unlike many filters in signal processing, don't go to great lengths to get a sharp transition between signals that are passed and rejected.
This washout behavior has several uses you could be referring to.  Your desired system might respond to changes in a sensor value it but ignores long-term position of that sensor.  Or perhaps you're building a PID controller and need a derivative term. The most likely case in my experience would be that you're building a complex control law, and at one point in building up that control law your math dictates that you need a washout filter.  The math for deriving that control law would be too complicated to explain here, especially in a broad case like an whole mode's lateral control laws.
In my experience, most work with a washout filter in an existing design is to adjust the gains going into it to make it more sensitive or less sensitive (and therefore the system will be respectively less stable or more stable). You could also adjust the time-constant of the washout filter, but to do so you'd have to have equations based on real-life data or system response models to find the new values for the time constants.
I've seen washout filters on vertical control laws, but I've never seen one used alone for lateral modes.  But I'm not some PhD student who's looked at over a hundred control laws, and it also could still be used for any of the applications listed above.  Brief googling says it might be used to filter out the constant yaw attitude in a yaw dampener, which would allow you to damp out yawing motions without forcing the aircraft to have no sideslip.  See this Aircraft Lateral Autopilots lecture slides from MIT for an example of that application.

A washout filter is used in a yaw damper autopilot to remove the steady state component from the yaw rate sensor. Feedback from the rate sensor is used to damp dutch roll mode, but during turns coupling between yaw and roll results in the aforementioned undesirable steady state yaw rate component. Detail is on pg103 of: this document

Good answer. +1 for linking an actual research paper

An interesting reference can be found in this MATLAB guide. Here, it is described as a method to prevent over-damping of the spiral mode of an aircraft. It is implemented by a zero at the origin (a pure integrator) and a single pole to limit its effect to low frequencies.
A good yaw damper will stabilise the aircraft around the Dutch roll mode (by reducing the bank/roll coupling). However, an overzealous yaw damper will prevent normal banking behaviour from an aileron input. The desired behaviour from an aileron impulse input is that the aircraft flies with a certain bank angle. This will result in a sideslip (damping needs some yaw rate to work, so sideslip/yaw is never fully prevented). The yaw damper will then also damp any tendency of the aircraft to return to zero sideslip (remember, a pure damper only looks at the yaw rate, and has no reason to have proper tracking behaviour to zero yaw). The aircraft's natural stability (for example, due to the dihedral) will then right the aircraft again.
A washout filter will integrate the yaw, and thus force the sideslip back to zero. This way, a coordinated turn is entered (assuming proper attitude control).

"A washout filter will integrate the yaw"  Isn't a washout filter a high-pass or derivative-like filter, not a low-pass or integral-like filter?  You might still be on the right track, but got that particular point backwards.

@CodyP As I understood it, it's a low pass filter to prevent desirable low frequency effects (transitioning to a turn) being filtered out from the aircraft dynamics.

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Why did this A320 stall protection demo not hold Valpha max?
This video is about the Airbus A320 High angle of attack protection

At 4:54 - 5:13 why did it pitch down? I know it is  trying to maintain Valpha max but if it would have stopped following Valpha max it was at around 200 knots and could have kept climbing at a very good rate. Instead it maintained Valpha max but when it maintained Valpha max the speed decreased and and it pitched down and thus the vertical feet per minute started to decrease.
I thought it was suppose to maintain the highest possible lift and if it stayed at 200 knots with the pitch up the aircraft was climbing at a very high rate but it pitched down and slowed the aircraft so it wasn't climbing at its max performance.

You need to look earlier in the video. At 3:59 the sidestick goes full back and full left. The aircraft exceeds the 33deg bank limit on automatic maintenance of pitch and bank, requiring the pilot to hold pitch and bank.

The pilot is in command from 4:54-5:13, not choosing Valpha max. He hits the bank angle and stall limits to demonstrate flight envelope protection, the point of the video.

So if the aircraft stayed at a 20 degree pitch angle the speed would have kept decreasing unitl it stalled correct, or would the speed stay constant at a point?

@GaryZenger The aircraft's flight envelope protection will not let the pilot stall the aircraft. It does not try to maintain a particular attitude with the pilot in control, it just prevents dangerous ones.

Suppose it was in alternate law.

@ymb1 At the time specified the aircraft was not at Valpha max, so the question doesn't make sense any other way. You were right the first time.

@GaryZenger Is that a question? Normal law accepts pilot input up to limits.

@Pilothead If the aircraft was in alternate law, where it doesn't have stall protection and the aircraft stayed at a 20 degree pitch angle the speed would have kept decreasing until it stalled correct, or would the speed stay constant at a point?

@GaryZenger Yes, the pilot would have stalled the aircraft but would have gotten audio and message warnings. This would also have required multiple failures of redundant systems in order to occur. All protections except load factor maneuvering are lost in alternate law.


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What is this Beechcraft bonanza A36 wing feature?
can someone explain what is this thing on leading edge of bonanza A36 aircraft.
Thanks

The feature is a dual vortex generator added to both wings to improve spin characteristics, which did not meet certification standards after the wings were lengthened to increase range by adding fuel capacity. These work opposite to stall strips; they keep airflow attached to the wing ahead of the ailerons. The vortex generated blocks the stall from the wing root from reaching the ailerons so that control is maintained in a spin, thereby allowing recovery in the required one turn.

The device, a dual vortex generator, resulted from Beech's efforts to improve the airplane's spin characteristics. During initial tests, the company found that the B36TC, with its long and heavy wings, would enter a rapid, nose-high spin to the right when loaded to aft-CG.

@Pilothead-- was trying to figure out from pics how far outboard it was attached--

@quietflyer If they were smaller and inboard they would have been stall strips.


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Can someone identify this crash?
I watched an episode of Air Crash Investigation or something else a while ago,  I want to know which one this was:
What I know is that during takeoff, the aircraft received a warning saying some part of the autopilot wasn't functional however they continued the takeoff as it wasn’t a big deal. They reset the flight computer, but since the aircraft was old and the flap settings and everything was set to normal, the aircraft began banking to the right and it crashed.

You might be referring to LAPA Flight 3142 (Episode 9 of Season 17). An alarm sounded during takeoff because the flaps were not set, but the pilots ignored the warnings. The aircraft failed to lift off the ground and crashed at the end of the runway.
If that's not the one, this list on Wikipedia should help you locate the episode.

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Why are autorotations to a full touchdown not practised any more?
What is the history behind a decision to discontinue helicopter autorotations all the way to ground contact? In the 1960s, our Army flight program directed full ground contact for any and all autorotations. I will never accept that 'simulations' are a substitute for actual practice. We were taught every possible aspect of autorotating a helicopter possible, including a vertical autorotation.

It may be a good Idea to add a location tag. from what I know of [Canadian cpl-h] this is only an American thing. every pilot from every other country I have talked to did full downs.

Too many broken off tail booms.  The Army can afford to replace damaged machines; flight schools that can barely afford hull insurance on recip helicopters in the first place, if at all, not so much.  (Funny story: I once asked an aviation insurance broker why the hull premiums on recips were so high, like over 5% of hull value back in the 80s (before Robinson's program).  He said, "Cuz they all crash!!!!" and laughed.  He said mainly it was because they are used for the most high risk activities: ab-initio training and Ag.)
Anyway, the FAA decided some years ago to remove the full auto from all but the instructor rating because, in a nut shell, it was calculated that the number of chopped off tail booms from training accidents attributable to full autos is way more than the number of chopped off tail booms from real full autos, where the hard landing could be blamed on removing the training requirement. Effectively, choosing one risk profile over another because the statistics favored it.
Not too different from ending the old practice of live engine cuts during multi engine training.  Except for a simulator, a multi pilot never experiences a real engine cut on takeoff until it really happens.  Back when live cuts were done, there were way more failure-to-maintain-control crashes in training than crashes from real engine failures.

I'm a fixed wing only guy but had a ride in an R66 last year, where I got to fly it around and hover it (after a fashion) and the instructor in command demonstrated a full auto for me.  It made me think of landing an airplane on a runway that was only a few feet longer than the airplane's minimum landing distance. Very little room for error.. in an R22, even less.

I think my phrase was misleading.  By "live engine cut" I meant inducing an actual failure with the mixture as opposed to zero-thrusting a still running engine.  In Canada at least, up until the 70s it was a practice to pull mixtures on climb-out and actually feather the engine.  A Piper Apache crashed at my airport outside Toronto in the mid 70s when that activity didn't go so well.

Dunno about the US.  I assumed it was similar to Canada.  When I did my multi, which only about 15 years ago, in Ontario, engine failures were "simulated" by the instructor/examiner zero thrusting the engine with throttle, then you did the drill by pantomime, moving to each control and calling out what you were pretending to do.  So you still had to cope with 50% power, maintain blue line speed etc. but the power was available.  The only time we actually feathered and unfeathered an engine was during a demo done at altitude.

for some values of "the Army can afford"...


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What does the letter J mean at the start of an FAA instrument approach chart identifier?
To identify a specific Instrument Approach Chart in either the FAA Terminal Procedures Publication (TPP), or the Department of Defense (DoD) Terminal Low Altitude (TLA) Charts, the FAA uses what they refer to as an internal numbering system.
This identifier on any given approach chart is found in the center of the top margin information area and includes two letters, A and L, followed by three or four numbers, followed by the approval authority for the chart, i.e.: AL-571 (FAA).
Found in the FAA Terminal Procedures Chart Users Guide and the general information legend in both the TPP & TLA, the "AL" stands for "Approach and Landing", however, on a high altitude approach chart, the AL is proceeded by a "J", i.e.: JAL-685 (FAA).
Does anyone know what the "J" stands for?
The chart users guide does not identify its meaning nor can I find any reference that addresses it. My assumption is Jet...but I would prefer to confirm what it stands for.

Since high altitude routes are called Jet Routes e.g. J501 or J88, I’d agree with you that it stands for Jet.

According to JO 7340.2J - Contractions p. 2-2-15 you're correct. It stands for "jet approach landing charts".


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What type of aircraft did these drop tanks come from?
I am trying to identify what type of plane my two recently acquired drop tanks came from. They measure 23" in diameter and about 12' long. Made of aluminum and "ALCOA" appears in raised letters on the rear end. Come apart into three pieces sealed by large o-ring style gaskets and have a metal rod that goes directly through the center of the three sections that screws together to hold the 3 sections together.
I looked all over the web as best I could and can't find anything that matches. Have two metal attachment points. No fins. Front more blunted. Rear more angular with small (5") removable tail cone that allows access to the main nut that allows the three sections to be separated (or mated and held snug). Fuel filler in front of attachment points. Very simple internal plumbing consisting of a fuel filter and a two short pieces of stainless tubing.
I believe they are at least 30 years old based on the story of the man I got them from.
I have embedded one picture of the tank, but there are more pictures available on the Ebay listing.

I'm putting this a comment because it doesn't answer your question but may provide more information to go with. ALCOA is an aluminum manufacture that was founded in 1888. They were a major manufacture during both world wars. At least you can know they were made by that company, its a start anyway.

It would help if you added the details here (including all the pictures), the EBay link will expire eventually, as will the images there. It would also help if you identified (here) where these tanks were found (be as specific as possible) and if there are any serial numbers on them or any other identifying marks.

@RonBeyer I believe low-rep users are limited to the number of links & embeds they can put in a single post.

Given the location in western NC I think it's safe to assume they are USAF drop tanks. Narrow it down to the a/c in use at the time at nearby bases and they are likely from F-15's or F-4's. Could be Marine as well, maybe A-4's out of Cherry Point. They have blunt tips, though. Maybe slower aircraft.

I've checked on the a/c mentioned and no match so far.  Additional ideas greatly welcome

Success - the tanks are from an F-80 Shooting Star.  Thanks to all who took time to assist me in ID-ing these tanks

It looks like they were used some on the F-80 like you said, but also on RF-80s, T-33s, F-94s, and Navy TO-1s, TV-1s.  They look similar to the Misawa tanks, but are different.
http://tailhooktopics.blogspot.com/2017/06/lockheed-pf-80-shooting-star-tip-tanks.html
https://commons.wikimedia.org/wiki/File:TV-1_Shooting_Star_at_NAS_Oakland_in_1954.jpg


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What is Full Fuel load and how does it differ from Fuel Capacity?
I've noticed that the fuel capacity is much higher than the full fuel load. For example in a Cessna citation 560XL
The Fuel Capacity is 6740 lbs
The Payload W/Full Fuel load is 960 lbs
Why is there such a difference?

The payload does not include the fuel itself. Payload means the total weight of all passengers, their baggage and all cargo on board. If you add this payload weight to your OEW (Operating Empty Weight), you get the ZFW (Zero Fuel Weight). On top of that you have to add the fuel.
The payload you quote is the maximum payload you can have if you also have full fuel on board. This is to make sure that the total weight of the aircraft remains below MTOW (Maximum Takeoff Weight) or possibly maximum taxi / ramp weight. If you fly with less than full fuel, you might be able to load more payload (as long as you stay below maximum ZFW).

Thank you for your answer.


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What is the difference between flight watch and home reserve?
Can anyone explain the difference between 'flight watch' and 'home reserve' with regards to flight and duty periods.
This is in regards to a charter operation, where crew members are on standby at the local crew house (home reserve), and are required to keep track of aircraft via satellite tracking while on standby (flight watch).
I am unsure what the distinction would be according to the law, as flight watch would still be considered as a duty period, as with standby time. Would the two be classified together as duty periods?
The reason this is of importance is crew members can do 12 hour shifts of Standby time , however the law has a different max time for duty periods

What jurisdiction?

This is for West Africa, under ANAC. They are structured as per FAA, however I am not looking so much as per the law regarding this, as per the generally accepted definition differences between Flight watch, Home reserve and Standby


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Do trailing edge vortices exist in reality?
Please don't talk about wing tip vortices and leading edge vortices(vortex lift)
Is it possible to see trailing edge vortices in real life, do they exist in reality?
How looks air in wake between wingtips, without flap, is downwash consistent or full of vortices? Theory predicts trailing edge vortices but where are they?
This two inboard white swirl is made by turbofan exhaust?

@sophit please don't answer in comments,  write a proper answer. https://aviation.meta.stackexchange.com/q/3553/19

Yes.  Most likely in a wind tunnel with smoke.  What you will see is highly dependent on Angle of Attack.
Ideally, any turbulence (that would be felt as buffet) is well away from the trailing edge.  What should be seen at AoA below stall angle, aft of the wing, is a strong downwash from the upper wing combining with the deflected airflow from the lower wing.
Air deflected upwards by the top of the wing is pulled down and accelerated by low pressure near the wing surface (just as the wing is being pulled up).  When AoA exceeds the stall limit, then downwash is insufficient and higher pressure "spills" over onto the top of the wing in the form of turbulence and vorticies, but this does not happen at lower AoA.
The trailing edge airflow pattern at lower AoA would be more like a "sheet" of downwash/upwash/downwash before it dissipates.
It is the downwash sheet energy that actually strengthens wingtip vorticies into the dangerous "tornadoes" that following aircraft may encounter.

Hoerner tips, end plates, and winglets are used to minimize drag effects from wing tip voticies, but that does not mean that planes that have them will not produce wake vorticies!.

Is it possible to see trailing edge vortices in real life, do they exist in reality?

Yes, it is.
The following picture from this report
just shows the development of trailing edge vortices not on the wingtip:

I think this comes from sweept leading edge. In reality trailing edge vortices dont exist,  their velocities all add up so you have consistent downwash in the wake between two wingtips.

I am asking myself if exist or not...Because I dont see them.

I think you are misunderstanding the term vortex/vorticity: it is not a tornado we are speaking about here but something as thin as the trailing edge+boundary layer. And the picture in that report does show trailing edge vortices as also written in caption. If you prefer a rectangular wing, that report has a picture also for it.

Can you post picture of straight wing  with trailing edge vortices? Dont use delta wings.

@JurgenM: as said, the picture is in the report linked in my answer.


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How to identify load paths?
How would you go on about identifying the load paths on an empennage structure, wing and fuselage?

@InsanityRules The answer given seems to be able to do it just fine. A broad question can be answered with a broad overview.

Look at where loads act on the structure. Then search for stiff structural members. Those will take most of the load. Load is proportional to stiffness, since deformation should be the same for adjacent parts. If it isn't, the structure has failed.

The simplistic explanation is that you design the aircraft shape, run computational fluid dynamics (CFD) simulations to get loads, then run finite element analysis (FEA) on the underlying structure to size the components.
CFD might look like:

FEA might look like:

Then when you have finished this sequential process you do it over again because after resizing the components the weight of the structure changes, so you have to change wing area to match the weight change, which makes the loads change, which then requires another component resizing.
You might wonder if it wouldn't be better if all these objectives were solved at the same time, and you'd be right. A newer design process is called multidisciplinary design analysis and optimization (MDAO) and is just becoming possible with modern, high power computing systems.
MDAO might look like:

where all the red buttons are control points that the optimizer uses to refine shape. You have to give the optimizer rules on how to proceed, which might look like:

If you want to read about MDAO one good source is Univ Michigan at
http://mdolab.engin.umich.edu/
Read a couple of their published papers and you'll get a pretty good sense of the complexity. MDO is the same thing as MDAO.
If you are interested in the optimizer, OpenMDAO is open source software. It is not aviation specific, though it was developed in conjunction with NASA. It is at:
http://openmdao.org/

Ah! Thank you, just what the doctor ordered :)

FWIW I help run the OpenMDAO project, and this answer is awesome! Cheers to you Pilothead


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What is a "slender delta" wing?
I am curious about delta wings. I read some articles and found the term "slender delta". Please help me to understand this term.

A slender delta wing is a delta with low aspect ratio.
The use I have seen is in the study of vortex lift, which is present at high angles of attack.
What is vortex lift?

Slender wing having a very high sweep angle which typically Λ>65°.
The non-slender wing is having low to moderately swept (35°–55°) wing planforms.


text:
What is the purpose for two nitrogen charged chambers in an oleo strut?
What is the purpose of a twin nitrogen charged chambers oleo, such as the one illustrated below? Why is it used and what are the advantages compared to a conventional mono-nitrogen chamber?
Training manual describes its operation as follow:
"Compression of the strut forces hydraulic fluid through the restrictor, thus pressurizing the nitrogen in the upper chambers and thereby absorbing landing shock loads. A flutter plate in the restrictor assembly permits an unrestricted flow through its controlling orifices during compression, however, flow is restricted during subsequent extension, thus eliminating any tendency to bounce during recoil."
While I understand the operation, it is not clear why this design solution was used.

Two chambers at different pressures creates a variable rate spring. Initial landing shock is absorbed by the low pressure chamber until its nitrogen is compressed to that of the higher pressure chamber, which then has sufficient volume to allow the desired amount of further compression at the higher pressure. The lower pressure chamber would have already consumed virtually all its volume.
The illustration is somewhat misleading in that the floating piston in the high pressure chamber should appear bottomed out when the strut is extended. There is no way for a fluid to be in equilibrium at two different pressures.


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What kind of jet fighter is this?
I visisited Tirana, Albania the first week in August. Outside a shopping mall called "TEG" there was an old jet fighter on display. I can't recognise what make and model this is. Can anybody here help me?
PS: I'm sorry about the poor qualities of the pictures, but there was hard to find an angle with free sight and it was far darker than it appears on the pictures.

Nobody is going to download zipped files from your private server, please host the pictures somewhere reputable.

It's a Chengdu F-7. Albania only had Mig 15 and 19. Look at the shape of the vertical stabilizer, pitot and body behind the canopy.

source

Correct, the J-7 (F-7 is another name for the same aircraft) is the Chinese copy of the  MiG-21F.

In his autobiography, Chuck Yeager noted that the J7 had a life of around 100 hours, though the Pakistanis managed to stretch that out to about 130. Apparently, they didn't expect it to last in combat, so they went for numbers instead of longevity. Probably why that one is on display... it's worn out.


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How do missiles steer (mainly air to surface)?
How do missiles steer in the air? What techniques do they use?

Exactly (by definition) the same way as an aircraft, identical to most airplanes as well.

Unclear as to whether the op is asking about how the control surfaces work, or how the missiles decide which way to maneuver.  it seems (to me at least) that the answer to the former is obvious, so op is probably asking about the latter.

Take a look at the following image. What do you see?

The Fins, Wings, and Canards, as seen in the diagram, work in a similar fashion to rudders/elevators/ailerons to develop drag to yaw/pitch/roll respectively.
Fins: Most missiles use tail fins which give extreme maneuverability and high angles of attack. Often they are fitted with wings to give extra lift and improved range. Maverick, Harpoon, AIM-9X Sidewinder are good examples of tail fin controlled missiles.

Seen above: Grid fins
Wings: Generally, wings play the same role as for an aeroplane by providing lift, and are the oldest type of control surface. Moreover, wings cannot work independently and in most cases are used as vortex generators to improve the efficiency of the fins. In addition, they are mostly used in subsonic cruise missiles like Tomahawk and Sparrow AIM-7. The problem is that the wings must be long enough to produce necessary lift.

Canards: They work more effectively with great maneuverability on low angle of attack, and work the same way as fins. However, located near to the nose of a missile, canards can cause a missile to stall at high angles of attack, which limits them to short range. Almost all smart bombs and laser-guided missiles use canards.
Furthermore, the split canard is a modern development (found in missiles like Python-4 and AA-11) which uses two canards, one of which is fixed, and the second is located just behind the first set and is movable. The role of the fixed canard is to develop high power vortices for the movable canards, for better performance at high angle of attack.
Source

Under "Wings," I don't think you mean the Sparrow, which is a supersonic surface or air to air missile with the common triangular "rocket style" fins.  Besides the Tomahawk, the US has used a series of winged, subsonic missiles or guided bombs including the AGM-86, AGM-129, and AGM-154.  Other countries have or had similar missiles.

Then there is also the old "BOMARC MISSILE", but it was definitely not an Air to Air missile.  Definitely had wings though.

minor correction... AIM 7 sparrow is supersonic.

Not sure how much detail you’re looking for, but most current missiles control their pitch, yaw and attitude via control surfaces that are actuated by electromechanical actuators. Some also use thrust vectoring of their rocket motor exhaust gases. The control system is typically driven by input from inertial measurement units (accelerometers, rate sensors and gyros), seekers and sensors such as radar and laser, and GPS.

Can you show me a picture or diagram please?

@Luke Justin, I just Googled "missile steering fins" and got a huge return.  There is no shortage of information out there, please look around and post questions only when you are genuinely stumped about something.

A unique variation on the control surfaces is the Starstreak missile:

Each dart consists of a rotating fore-body with two canard fins attached to a non-rotating rear assembly which has four fins. The rear assembly of each dart also houses the electronics that guide the missile, including a rearwards facing sensor.

The sub-munitions steer by briefly decelerating the rotating fore-body with a clutch. The front wings then steer the missile in the appropriate direction.

Not really an answer, but I think it's relevant:
You look at an airplane, you see big honking wings and tails.  You look at a missile and you see stubby little things.  What you don't realize is that they're the same thing.  Airplanes don't need big honking wings to cruise, they need them to fly at low speed for takeoff and landing.
A missile, however, will be launched from an aircraft already moving along rapidly, it never needs to be able to fly at low speed and thus the fact that the wings are utterly inadequate for low speed flight doesn't matter.  Most missiles have minimum launch velocities that are far above normal runway speeds.
Yes, some missiles are capable of taking off from the ground, this is done by boosting them into the sky on a separate rocket booster that then falls away and allows them to fly normally.

Missiles steer either by commands from internal computers, (for Air-to-Surface missiles with GPS or Inertial navigation systems), by commands from a ground radar station over a datalink (SAMs such as SA-2, SA-3, use this technique) or, (for missiles designed against moving Air-to-Surface or Air-to-Air targets), by using Proportional Navigation. Proportional Navigation basically just locks a gyroscopically stabilized seeker head  onto the target (by centering a sensor on radar, infrared or video energy, (AGM-65 Maverick), coming from the target), and then turning the missile in the same direction as the Line of Sight (LOS) rate of that seeker head (as measured by the gyroscope), until the LOS is zero'd out. If the LOS rate is zero, you are on a collision course.
The proportional in the name comes from the fact that the turn rate commanded by the electronics is not always the same as the measured LOS rate. Missiles that know the rate of closure with the target adjust that proportionality constant. The higher the closure, the harder they try to turn. Missiles that do not know the closure, use a fixed (constant) proportionality ratio. The AIM-9 Sidewinder, for example, commands the missile to turn at 4x the measured LOS rate. This design, in fact, is responsible for the missile's name. When launched it is still relatively slow, and must pull a lot of lead on a turning target to zero out the LOS rate and intercept. As the missile accelerates, it needs less lead, and turns back into the the target, then, after the motor burns out and it begins to decelerate, it needs more lead again. The end result is a snaking flight path, like a rattlesnake.
Radar missiles, that are aware of the closure, eliminate this inefficiency by tailoring the proportionality constant so that the commanded turn rate is lower at low closure rates.


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What navigation systems were used by the Space Shuttle during reentry?

What equipment did the Space Shuttle orbiters carry to support navigation during reentry?
Were there any differences between the individual orbiters in this regard?

I think this should go in the Space Exploration Stack Exchange.

If there is a "space-shuttle" tag in the Aviation forum then I would say it is appropriate here.

Navigation in space would be off topic here. If you're asking about navigating during approach and landing, it's on topic here, related to Was the Space Shuttle landing sequence executed manually or automatically?

Agree with @fooot. Need some clarification from the OP. Until then, it appears to be quite off topic.

Do you have a reason for believing Columbia's navigational equipment was different? I gave a general answer below which discusses the orbiters collectively.

Also agree with @fooot. Since it was posted here on Aviation, I assume the question is in regards to navigating to the landing site, and I edited it to reflect that. I think it's on-topic. If the OP was asking about space navigation, they can ask a more specific question on Space SE.

I meant navigation is general. as in, including take-off and landing :)

With the exception of GPS upgrades, I don't believe there were any substantial differences in navigational equipment between the various Space Shuttle Orbiters for most of their operational history.
Each space shuttle had:

3 Inertial Measurement Units
3 TACAN receivers* see GPS Upgrades
4 Barometric Altimeters
3 MSBLS Receivers
2 Radar Altimeters
2 Air Data Probes
Star Tracker (on-orbit)
Rendezvous Radar (on-orbit)

There is lots of information about the Shuttle's navigational equipment in the Shuttle Crew Operations Manual.
GPS Upgrades
In the early 1990s, it appeared that TACANs were going to be phased out, so NASA began evaluating GPS as a possible replacement. Space Shuttle Endeavor was the first to have a single GPS receiver installed in 1993, followed by the other shuttles beginning sometime around 1996.
By 2002, each shuttle had 1 GPS and 3 TACAN receivers. The plan was to remove the TACAN receivers and install two additional GPS receivers - resulting in a 3-string GPS system. However, after the loss of Columbia in 2003, it was decided that the Space Shuttle Program would be discontinued in 2010 (later extended to 2011), and therefore it wasn't worth upgrading all three remaining shuttles. Only Endeavor was upgraded. Discovery and Atlantis continued to fly with 3 TACANs and 1 GPS for the remainder of the program.
You can read a lot more about the history of the GPS system here: Operational Use of GPS Navigation for
Space Shuttle Entry.

thanks a lot :)

https://www.nasa.gov/centers/johnson/pdf/390651main_shuttle_crew_operations_manual.pdf , this link answers it all for me !!! thanks a lot!


text:
What exactly do fighter pilots do during peacetime sorties?
I am located near a base with a Sukhoi Su-30 squadron of the Indian Air Force. These jets keep doing these sorties every day and night. I have always wondered what exactly these jets do during their sorties. I thought it was always about training, but I found out that the basic training for these pilots happens elsewhere.
Hence, what exactly happens on a normal day with these trained pilots and their jets?

Training doesn't end the moment you get your license

As with any job, there will be some initial training to learn the basic skills needed, and that is typically done at a central location. But there will also be ongoing practice to maintain those skills and continue to improve them. Modern fighter jets are complicated machines and take a lot of knowledge and practice to operate. Simulators and classroom learning help but can't completely substitute flying and maintaining real aircraft. In the US, military aviators get about 20 hours per month of flying time. There's a saying in sports that "you play how you practice." When these pilots go into battle, lives are on the line, and they want to be able to recall skills they practiced recently, not years ago in basic training.

Recent training (proficiency) is an important facet of mission readiness.  Basic training is important, however, it may be done in another country (Americans train partner countries in the US) and hopefully it is apparent that follow-up training is critical in the homeland.
What is not visible is the training that happens behind closed doors in simulators and the classroom.


text:
What are the FAA regulations on grass airstrips?
What are the FAA regulations on grass airstrips like grass height, lighting, necessary aircraft equipment, and the like?

If you're asking where to find these regs, I think this question is entirely on topic.  If you're asking for them all to be listed here, I think the question is too broad.

I went poking around the FAA Regulatory and Guidance Library until I found FAR 139.307, which states:

Sec. 139.307
Unpaved areas.
(a) In a manner authorized by the Administrator, each certificate
  holder [must] maintain and promptly repair the surface of each gravel,
  turf, or other unpaved runway, taxiway, or loading ramp and parking
  area on the airport that is available for air carrier use as follows:
...
(b) FAA Advisory Circulars contain methods and procedures for the maintenance and configuration of unpaved areas that are acceptable to the Administrator.

So I went looking for those advisory circulars.  There are probably more that I haven't found, but AC 150/5300-13A - Airport Design beginning at page 82 seems to have the sort of thing you're looking for.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What are the main factors that make an aircraft have good STOL performance?
What are some of the main characteristics and design principles utilized to make an aircraft have good STOL performance?
As a bonus, what are some disadvantages to some of those characteristics and thus reasons why they aren't utilized on all aircraft design (cost aside).

because for most of the intended use case it's a waste of money

Weight, weight, and weight. As attributed to Colin Chapman, Lotus F1 car designer, "simplify, and add lightness". Good philosophy for aircraft, too.

Good STOL performance is directly linked to how slowly an aircraft can fly and how quickly it can accelerate and decelerate when on the ground.
Low wing loading (a lot of wing for a given aircraft weight) with a lot of camber is the primary means for attaining slow flight. It is not used for every aircraft because a big, cambered wing creates more drag than a small wing, which limits top speed. Flaps and slats can help by modifying the shape of the wing to provide more lift when flying slowly while keeping drag low when retracted for top speed. These add complexity and weight so they are used by aircraft needing speed.
Rapid acceleration requires power, which costs money and is heavy. You pick how much you want. Rapid deceleration usually depends on brakes. It is limited by friction between tires and ground, and sometimes by aircraft configuration. Most every aircraft has brakes strong enough to make a tire skid.
Google "valdez stol competition" to see the world's shortest takeoffs and landings. These guys practice a lot, and you can see some of them nearly flip onto their noses by how hard they brake.


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What is the loading diagram for a C-130J?
I'm a student participating in a design project wherein we have to develop a paper design for a payload to be airdropped from a C-130J.  Naturally, I'd like to look at the weight and balance of the C-130 to see what sort of limitations we have (since we'd like to literally fill the cargo bay with multiples of this payload), but it does not seem to be available anywhere.  I found a CNI-MU emulator on Google Play that gives some basic information (basic weight/arm, crew weight/arm, fuel weight/arm), and I have a loadmaster form from the 2015 Defense Transport Regulations that shows me the cargo hold layout. However, something's not lining up.
The default information loaded into the emulator places the basic weight at STA 730 and the fuel at STA 750, which is roughly where the aircraft ramp begins according to the DTR cabin layout (which labels it as corresponding to the B/E/H models, but, according to the DTR, it applies to the J model as well), but it seems strange because, according to the CNI-MU emulator, that's around the quarter-chord of the wing, which is a little behind the center of the cargo hold.
In other words, I'm a bit confused and am looking for anyone who might be able to either make sense of the above or answer the following question:
What is the loading diagram for a C-130J (i.e., what is the basic weight/arm, crew arm, fuel arm, and payload stations within the cargo cabin)?

Hi Marius.  Welcome to Aviation.SE.  I'm sorry to say that I have voted to close your question.  I think it's a good question but needs very specific expertise to accurately answer.  I am fairly certain that you will not find that expertise here.

Why don't you ask where the load should be relative to the wing? This way you don't need the specific C-130 J diagrams but gain knowledge which can be applied to all aircraft.

I respectfully disagree with @Simon. I believe it to be a reasonable question. The difficulty is locating the basic information. If you really want to understand what's going on, you need not only that mentioned in your last sentence in bold but the monocoque limits, the linear limits, the lateral imbalance limits, as well as whatever might be unique to C-130 weight and balance. What you need is the equivalent for the C-130 to what you will find for the 747 at http://terryliittschwager.com/wbmanuals.php.

@PeterKämpf -- agreed: the important thing is the placement of the aircraft CG.  However, given my past experience in aircraft, I figure that this is generally located in front of the quarter-chord...but, in order to load this particular aircraft such that that occurs, I need the weight and balance information for the aircraft, as mentioned by Terry.

I would agree with @Terry. Just because we don't currently have the expertise at the site to answer the question doesn't mean it should be closed (we're not in beta anymore! :). Some day, a C130 load master might just stop by and answer this. Probably too late for the OP, but it will be nice to have the answer somewhere on the interwebz.

goto C-130 Hercules.net maybe they can help out.

@radarbob -- good call.  I found that place after I went here and am in the process of getting a more full response...in the meantime, I actually figured out the issue myself and have the correct load stations.  Should I just post the answer here?

yes. post self-discovered answers, and mark it as your preferred, if in fact it is.

As listed on a CNI-MU emulator designed for use by C-130J loadmasters, the following is a list loads and moment arms for the aircraft:

Basic weight: 80,000 lbf/STA 530
Crew weight: 600 lbf/STA 153
Fuel weight: 38,000 lbf/STA 551 -- this weight is, naturally, variable,
although the moment arm appears to stay relatively constant.
CG limits: 21-30% MAC

Finally, payload moment arms can be determined via use of of DD form 2130-2 on page III-V-17 of the 2015 Defense Transport Regulations (http://www.ustranscom.mil/dtr/part-iii/dtr_part_iii_app_v.pdf).

Congrats on finding it, and thanks for coming back to post!

Sorry I saw this late. I am a C-130J Loadmaster and teach the course to Air Force students. I am on my mobile, but can answer more later. For a quick answer though, you are mixing up two variants of the -J. The -30 is a stretch, and those are the numbers you found. Flight station 737 is at the ramp on a short model. The -30 is 200" longer however. The mean aerodynamic chord of c-130 any variant or model is 164.5". Leading edge to MAC of a stubble is 487.4". -30 LEMAC is 687.4"


text:
How does wind affect takeoff weight limits?
Two days ago I took off from BUR in relatively windy (although dry) conditions. Flightradar showed departure from runway 33, and winds were recorded roughly mid 20s kts from the N-NNE direction. Temperature was mild at mid-60s. The aircraft was a B739.
Prior to door closure, after everyone had been seated, the captain asked for two volunteers to take a different flight. His reasoning as explained to us involved a combination of the windy conditions and the length of the plane (not stated exactly as such, but in a nutshell involved these two factors). The crew did not specify a section of the aircraft that the volunteers needed to be from, nor did they reshuffle passengers after two volunteers left. It was a nearly full flight, but not overbooked as everyone was already seated.
My confusion is why a plane taking off into strong headwinds would require less weight, when headwinds theoretically reduce runway takeoff length requirements and make takeoff easier, generally speaking. Because the captain mentioned the length of the plane as a factor, and knowing that the 739 has some more significant tailstrike risks, my hypothesis is that the nose pitch and/or flap setting in windy conditions has something to do with it, but I can't fully understand why. Can anyone explain why two passengers needed to be removed?

If the weather was also windy at the destination airport, it could’ve been that the pilots wanted to take more fuel for holding with them, more fuel = less payload. But that’s just speculation.

Two passengers, say 180 lbs each, 360 lbs plus lets say two 50 lb bags each, so 460 lbs total = 76 gallons of fuel. Just a fraction of the fuel carried, 7,837 US gal, or <1%. Doesn't seem like available fuel would be the issue.  Similarly, 460 lbs is just a fraction of the Max Take Off weight o Max Landing Weight, 187,700 lb and 157,300 lb.

@CrossRoads yes but perhaps they were several thousand lbs below MTOW at the original fuel load, but decided due to higher headwinds they needed to add a couple thousand pounds, which forced a reduction of ZFW by 500 or so to stay under MTOW.  Who knows, but that sort of scenario is the only thing that makes sense.  I'll also guess that if the reason was given by the FA or gate agent after being told by the capt, the story morphed a bit in the retelling.


text:
How can I convert a Peruvian pilot's license to one that will let me work in the USA?
My fiancé just became a U.S. resident. He's originally from Peru and is a helicopter pilot with some airplane experience as well. He has more than 8000 hours flying helicopters and around 150 airplane hours. He's an instructor pilot in Peru and currently works for the Peruvian Air Force.
I would like to know what does he has to do in order to work in the United States. Is there a different certification he has to get in order to fly either a commercial plane or an helicopter? Where can i get more information about it?

Welcome to aviation.SE! I think this is a possible duplicate of What are the requirements to convert a license from Iran to USA? The situation described in that question seems very similar to your fiancé's situation; I suggest you review it - including the linked questions - and see if it's helpful. If not, it would be great if you can edit your question or add a comment to tell us what information you still need.

Well, first step would be a validation of his PPL, resulting in a US PPL based on the foreign one and only valid with both present. This can be done at an FSDO (Flight Standard District Office) for free. It can be done by mail as well. Also many flight schools experienced with foreign students can arrange it at a fee (usually in the 50 USD range). Going through a flight school may be the fastest way - for a CPL he needs one anyway. (Reference)
A foreign CPL (and everything else but a PPL, so like an FI) cannot be converted or validated. He will have to go through full process as described in 14 CFR 61.123. This needs signing up to a flight school/instructor. So while his hours will be accounted for, he need to do at least an extensive check ride (usually more than one - as procedures may differ) to convince the instructor to be ready for the practical test, as well as going through all knowledge tests required - and fulfil the language requirement as well.
A (good) school may also be the best place to get more in depth information, as this case may hold many individual details to be considered.
I guess the worst part might be to (re-) learn the standard phrases used in the US vs. what is used in his country of origin. 8000 hours means a lot of experience and deep entrenched radio phrases :))


text:
Where can I find drawings or diagrams of the Boeing 737-800's internal layout?
I am working on an alternative fuel system for my final school research. I am applying it to the 737-800. Now I could not find info on how the internals are situated. Of course pictures of the cabin are widely available. However I am looking for drawings, pictures or graphs on the cargo compartment, systems placement like gear, hydraulics, pumps or whatever. Basically the whole internal volume and what it is occupied by.
This is maybe a bit demanding but any info is really helpful.

This is a Q&A website, thus you may ask a clear and specific question (e.g. where can I find drawing and blueprint of B737-800?)

Thanks for the feedback. If there are blueprints that show internal space division, then yes please! I would love to see those.

I think the question is quite clear, although documents more specific than @Daniel's answer may be hard to find. A "how it's made" 3D picture with cut-away drawings of the internals may be your best source, even if you have to estimate some of the dimensions.

Some of this information is in the aircraft maintenance manual (AMM) (example).

Check out the "Airplane characteristics for airport planning" document for the 737, espcially from page 47: http://www.boeing.com/assets/pdf/commercial/airports/acaps/737.pdf
These kind of documents are created by the airplane manufacturer and are often publically available.


text:
Are the single-engine Piper Malibus required to have a black box?
Is the single engine Piper Malibu required to have a black box?

Required by who, the operator, the FAA, the EASA?

Jimy, I am not sure.  I have been following the story of Argentine soccer player Emiliano Alva who was traveling in a Piper Malibu on Monday, and the plane has not been located.  The FDR and CVR have never been mentioned, so I just was curious as to why.  Thank you for your comment.

The short answer is that it probably does not require a "black box".
What you refer to as a "black box" is actually 2 things (and Orange!) a Flight Data Recorder and a Cockpit Voice Recorder. The rules on when they are required is broadly similar, however the data required to be captured by the FDR varies.
For the CVR:

Fixed-wing aeroplanes with a maximum take-off mass of more than 5 700 kg and for which the certificate of airworthiness is first issued after 1 January 2003 shall be equipped with a CVR with a recording duration of two hours

For the FDR:

[...] depending on the maximum certificated take-off mass and the date of first issue of the individual certificate of airworthiness. For example, provision 6.3.6 of Annex 6, Vol. I states that, all aeroplanes of a maximum certificated take-off mass of over 5,700 kg for which the individual certificate of airworthiness is first issued after 1 January 2005 shall be equipped with a Type IA FDR

The Piper PA-46 (aka Piper Malibu) has a MTOW ranging from 4,340lb(1,969kg) to 6,000lb(2,721kg).
Speculation about the recent incident, and the specific model intentionally left out!

Jamiec, Thank you for your comment.

5800kg? How did that number become so golden? I'm just curious as these things sometimes have an interesting backstory.

@Dannie 5700kg is (more or less) 12,500lbs, which is the FAA's regulatory definition of a "large aircraft" and also means that a type rating is required. See this question.


text:
Can you be a pilot after being diagnosed with Generalized Anxiety Disorder?
Went to my primary care physician who referred me to the psychologist. Went in for two evaluations. The only thing that had been written on my medical record was anxiety, no medications of any sort had been prescribed and the psychologist asked that I enrolled in anxiety classes in college (this was during my freshman year) I am a sophomore now.
Was wondering if this diagnosis of anxiety could prevent me from obtaining a third class medical, although it is not listed as anything that requires an FAA decision especially if no medication has been taken or prescribed.

Psychiatric conditions can't be diagnosed by objective means (such a blood analysis or a radiograph). Any pilot confessing such a condition, specially before an aviation medical examiner, risks losing his license.

Real question is "should you be.... " Imagine yourself in a bad situation during a flight, would you be able to keep calm and act rationally or you'd have a panic attack? If in your country free practicing doctors are bound to secret you should try to understand this with the help of one for your safety.

The first thing is to determine if you were evaluated for anxiety, or diagnosed with an anxiety disorder.  Your primary physician's office can answer that because it will be in their records.
Often (not necessarily applicable in your case) symptoms which do not require ongoing therapy or medication may not have hard diagnosis.
Avoid assuming that you have a disqualifying condition.  Contact your physician and ask if you have that diagnosis.  It might help to explain why you are asking, specifically that you would like to fly and get an FAA Medical, so that they know the context of the question.
You might also want to read this FAA writeup on Item 47:
https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/app_process/exam_tech/item47/et/
As a final note, as an instructor I have had several students over the years who had serious, diagnosed psychiatric issues.  Most of them got effective help. A few became ineligible for a FAA medical. One refused to seek treatment as they were concerned about losing their medical. (I discontinued providing instruction, which aggravated the problem.) However, I know of no pilot or pilot wanna-be who had to take a class on anxiety or anger management, or personal relations, or similar to be denied an FAA medical on that basis alone.
In your case, the anxiety may have been situational, and developmental (as an adolescent) and clarifying whether you have a diagnosis (as opposed to just an evaluation) before you spend the big bucks for an AME exam would be appropriate.

The authoritative answer to your question can only come from an Aviation Medical Examiner - an AME, or "flight doc".  An internet message board is the wrong place to consider all the specifics of your history, and as far as I know we don't have any AME's who participate here.
My expectation is that the answer you'll get will be in the category of, "yes, provided that you accomplish the following..."  What tests, evaluations, observations, or whatever else that entails may range from very minor, to very lengthy & costly. From what you've written, I doubt it would be horribly difficult, but my opinion is from one non-MD guy on the internet, and it's worth slightly less than what you're paying for it.
If flying is something important to you, then you really owe it to yourself to get the authoritative answer from the only source whose opinion counts: make an appointment to talk to an AME.

Hmmm... telling somebody with a medical question that his best answer will come from an AME, gets down-voted? Okaaaay...

I am not am AME, but in section 18m of the application for the medical you will be required to disclose if you have been diagnosed with this condition. That is a significant flag to AME's under the guidelines for evaluating psychiatric conditions. The examiner will only have two options at that point: to deny your medical application, or defer it to FAA Aeromedical. If it is deferred you will get a letter from Aeromedical telling you what evidence you have to submit for evaluation.
Note that the application does not ask if you are taking medication for the condition, only if you have ever been medically diagnosed to have it.
The bottom line is that you should discuss this with whatever AME you have selected to work with before you submit the application.

That is not correct. Anxiety with no history of requiring medication-- the AME can Issue and that's before we even get to talking about whether this is a diagnosis or not. Not every YES answer to 18(m) means a denial/deferral. Talk about giving someone anxiety.

You are not correct and your evidence does not support your argument. I quote from the Aeromedical guidelines: "Any affirmative answers to Item 18.m., Mental disorders of any sort; depression, anxiety, etc., or Item 18.p., Suicide attempt, are significant." Notice there is no mention of medication. The link you posted doesn't even reference the issue of anxiety disorder.


text:
Where can I find more about a cargo pickup technique that doesn't require landing the plane?
A number of years ago, I read about a technique for cargo pickup and recovery at remote sites using a low-and-slow-flying plane.  The plane would enter a slow orbit around a point on the ground and lower a bag to the ground on a long (hundreds of feet?  A thousand feet?) line.  Once the bag was down, the plane would maintain its turn around a point so that the line stayed slack and the bag stayed in position.  Cargo (perhaps mail?) could be retrieved from or placed in the bag, then once the transfer was complete, the plane exits the circle and lifts the bag.  I'm a lot less clear on that part.
However, I don't have any idea where I read about this, and haven't been able to find any more descriptions of this.  Can anyone tell me if this technique is real, what it's called, where/when it's been used?

This title probably isn't great, either--it's not THAT similar to the skyhook, but it's what comes to mind.  Would appreciate help there.

Surprised to see this question getting love three years later, but after some initial "who moved my cheese" skepticism I like the new title.  Thanks.

I like cheese...

See the notes on this page under the "Delivery" section. Looks like its formally called " long-line loiter". There is a brief note on it here and a US Patent here and this manual from the 70's that seems to show how to do it and some related research on it.
Here is a nice image of the maneuver

Brilliant.  There's a ton of information in the military "manual", which is actually a report on the feasibility of retrieving personnel via this method.  Spoiler:  <2G max acceleration!

Happy To Help !

Most people credit it to Nate Saint's technique (and it's probably been rediscovered many times), but there are much earlier references.
Popular Science, December 1934:

...at Tulsa, Okla.  Circling an air field at 1,500-foot altitude, [A. V. Muzzey, credited here as inventing the technique] lowered a sack of eggs safely to the ground, and hauled aloft a live chicken that a ground assistant attached to the cable in exchange.

And, although it's not technically long-line loiter, a patent from 1942 using multiple aircraft:

Wonderful answer.  I hope you and the community will indulge my edit, which elevates a quote from the Popular Mechanics article about the chicken/egg exchange into the answer text.

I don't know the name of the technique, but I know Mission Aviation Fellowship  pilots used it in Ecuador in the 1950's. You can achieve a similar effect by whirling a the end piece of dog-chain or similar hanging from your hand around in small circles. The chain will form a bow shape, and the bottom will stay roughly in the same place.  Hand = plane, rope = chain... put the bucket on a swivel... Changes in speed or hand orbit can lift the end of the chain.
Wish I could fly like that...

Developed by the USAF Aeronautical Systems Division (ASD), the gunship
  applied a principle adopted by bush pilots in South America. This was
  the use of a weighted bucket suspended on a rope from an aircraft
  flying a very tight continuous turn to keep the bucket stationary at
  the tip of an imaginary cone for the collection of mail and the like
  from inaccessible sites.

Source: Defenders: a comprehensive guide to the warplanes of the USA, Oriole, 1989.

I saw a similar technique to pick up personnel. A balloon was floated up, and a plane with a big V in front collected the line and pulled the person up.
Pictures and more description here CIA's Fulton surface-to-air recovery system (STARS)
This was used in a couple of the early James Bond (007) movies also.
Similar can be done to what banner tow pilots do.  A line is strung between two poles, the plane flies above with a hook on a rope to grab the line and then takes off full power, with lots of slack to give the plane time to climb and gain some speed before the load's drag kicks in.

The Skyhook method used to be mentioned in the title, and is explicitly not what this question is about.


text:
Are airport emergency vehicles' sirens louder than normal?
So there I was this afternoon, sitting in my car waiting on my wife's flight to get in to Dulles Airport (IAD), in the cell phone parking lot. I was listening to some music on the radio when the rescue vehicle (ambulance) got a call to go somewhere. I know this, because it absolutely deafened me. Turns out (one of) the firehouse is right next to the lot. I've been in front of firehouses before when trucks have gotten calls and they weren't THAT loud.
This started me wondering if airport emergency vehicles have extra-loud sirens, due to the greater than normal ambient noise on an airport?

Unable to get complete answer. The best I could find: FAA regulations stating "The siren
speaker will be rated at 100 watts minimum". (3.10.6.1, page 65) The DC regulations say a siren on an emergency vehicle must be "capable of giving a signal audible under normal conditions from a distance of not less than five hundred feet". (712.2, page 1) Unsure how to convert between them.

A 100W speaker can provide an audio signal around 120dB. Which is almost twice as loud as a home TV turned up to maximum volume. at 85dB staying near the vicinity of the source would damage your hearing

If you really want to move the traffic out of the way, use a Federal Q2B electromechanical siren. 128 db and so loud it's banned by the FDNY for being too loud.

Airport emergency vehicles are not required to have louder sirens than off airport vehicles, at least in the US.
Emergency vehicle sirens conform to standards from various entities, one of which is Federal NIJ Standard-OSOl.00. Two levels are specified, Class A and B. Class A is

A-weighted on-axis sound level of 120 dB and meet the off-axis sound
level and other requirements of paragraph 4.3

Class B has the same requirements at 115db. Louder class A sirens may be mounted in less than optimal locations as under a hood. The less powerful Class B must be mounted in an unobstructed location, as in a forward facing roof mount.
Airport emergency equipment with a siren is required to have a 100w rated speaker if purchased using Federal Airport Improvement grant funds, which pretty much means all of them will conform.

3.10.6.1 Siren. The vehicle will be equipped with an electronic siren system. The amplifier unit will include volume control and selection of "Radio," "PA," "Manual," "Yelp," "Wail," and "Hi-Lo" (European) modes, and a magnetic noise canceling microphone. The amplifier, microphone, and controls will be within reach of the driver and the turret operator. Siren activating foot switches will be located in front of the driver and the turret operator. The siren speaker will be rated at 100 watts minimum and will be located in a guarded position as low and as far forward on the vehicle as practical.

Looking at an example manufacturer's products, every siren had a 100w rated speaker and conformed to a Class A rating, so these seem to be functionally identical in performance. I found no Class B sirens; there is likely little difference in manufacturing cost and so does not justify an installation constraint.


text:
Is it possible to drive a prop directly from a jet engine without a gearbox?
I'm studying turbojets, turbofans, and turboprops. I can see that, for the latter engine configuration, a gearbox is necessary so that the propeller rotates at a lower velocity than the main compressor. Here is an image:

For the experts in the aerospace field, my question might be regarded as a bit "odd", but here I go: is there any reason why we can't use a second turbine to move the propeller with coupled shafts, instead of relying on a gearbox? The idea would be to use a low pressure turbine that moved the propeller.
I think this might be unfeasible, because the added weight of a second turbine would be higher than the weight of the gearbox itself, but I don't know if there are additional considerations to this.
But on the positive side, we would have the following (and please, correct me if I'm wrong):

Less maintenance work.
Propeller rotation shaft aligned with the main engine core (does this even represent an aerodynamic advantage?).

EDIT 1
The idea would be using two turbines. A high-pressure turbine (HP) that moved the compressor, and a low-pressure (LP) turbine that moved the turboprop. My idea was taken from the turbofan engine config.

EDIT 2
As the user mins pointed out, we would need a very slow turbine or even a gearbox. But we could design the LP turbine with few stages (say 1, 2 or 3) so that its rotational velocity would be low enough as to move the propeller without having aerodynamic losses in the tips of the prop. And as this same user pointed out, there already exists such a configuration (see here). The question then is, why isn't this configuration preferred over the "conventional" one? (i.e. the one that uses a gearbox).

What do you mean by a second turbine? If you just mean another shaft, that's how most turbofans work.

I mean a second turbine (or a low pressure turbine) that moved the propeller. I'll make that clearer on the question, thanks.

The high pressure (HP) turbine would move the compressor. The low pressure (LP) turbine would move the propeller.

Added an edit to make it clearer.

It can work for a fan (turbofan) because the rotating speed of the fan is high compared to the propeller. A propeller would need a second turbine very slow... or a gearbox.

But you could build it with few steps (say, 1 or 2 or 3) so that it rotates slow enough so as to move the propeller and save weight. Isn't this feasible? Why?

Gearboxes are easy,  cheap,  and effective. Turbines really complicate things.

Hey @mins, thanks for that link. I edited the question at the end (see EDIT 2). The question is still in the air!

Hey @RonBeyer, if I'm not wrong turbines require much less maintenance work after it has been built than gearboxes. It's not clear, in my opinion.

Ey @mins, that first post was also mine hehe, but it doesn't exactly explain why a turboprop can't be configured with a second turbine, which is my exact question here.

Thanks, if you find a way to write your insights/answer in a separate answer I'll accept it.

Thanks @mins, let's wait for an answer then, can't wait to know it.

As a side comment, there is a type of engine researched in the 80's/90's, but never marketed, where an unducted fan is driven directly by the turbine shaft without a gearbox: The propfan. It's close to your idea, albeit the unducted fan is not exactly a propeller. Safran has restarted researching on this design, end of 2017, for an operational use after 2030.

Two counter-rotating unducted fans on a free turbine engine (source)
Having discarded the propfan, let's go to the actual answer!

Short answer
A propeller rotational speed doesn't exceed 1,000 or 1,500 RPM (it depends on its size too). The slowest shaft of a jet engine spins in the range of 5,000 to 15,000 RPM, sometimes more. A reduction gear is used to compensate for the difference.
A fan may spin at 5,000 RPM, however the use of a reduction gear is also desirable, though it is often avoided by limiting the speed of the core, at the expense of a loss of efficiency. New aircraft like the A320 NEO can be fitted with geared turbofan engines, for better performance.
The reason the turbine cannot spin at a lower speed is that a low speed means low torque, a problem common to many air-breathing engines (maybe except the free turbine).

Dotted line: Theoretical torque at low speed. Plain: Actual torque. You may compare with trying to pull away in a hill in fourth gear.
Low torque also means increased spool up time, a drawbacks that is often a no-go factor.

Details
Jet engines must rotate at high speeds by principle, as a lot of air must be compressed to burn a lot of fuel in a small amount of time. On the other hand the fan or the propeller are more efficient at low RPM.
Let's see how engineers have dealt with these two opposite needs in different engine types.
Single-spool turbofan
The simplest design is the single spool engine (all discs rotating at the same speed). While this is possible, the output shaft is at a high rotational speed. This is usable for a fan which also rotates at high speed. The core compressor is not as efficient as it could if it rotated faster.

The Snecma M53-P2, used on the military jet Mirage 2000, has a rotational speed of 10,600 RPM.

Better efficiency can be achieved by increasing the compressor speed and reducing the speed of the fan. It requires the use of a distinct second spool.
Two-spool turbofan
Such configuration is used in many turbofans (Rolls-Royce being a notable exception with a third spool). A low-speed / low-pressure turbine drives the fan and usually the first stages of the compressor.

From this EASA certificate, the CFM56-7B used on all B737 NG has a maximum HP shaft speed of about 15,000 RPM and a LP shaft speed of about 5,400 RPM.

Increased efficiency needs to further increase the fan diameter but also to slow down the fan to keep the linear speed of the tips at a reasonable value. A slower fan will not be directly driven by the turbine.
Geared turbofan
Slowing the LP turbine adds complexity and also creates a problem: The output torque also decreases (which is a phenomena in all mechanical engines). This leads to increased reaction times after thrust requests, with also means less safe engines. A gearbox is used to prevent sacrificing the precious torque. This unusual configuration is an option on the A320 NEO.

PW1000G (formerly known as project GTF) has a HP shaft at 20,000 RPM, a LP shaft at 15,000 RPM, and the fan connected by a 3:1 reduction gearbox rotates at 5,000 RPM.

planetary reduction gearbox 3:1 (source)

If the altitude is sacrificed for other benefits and the engine is used in denser air, then a turbofan is not anymore an efficient solution.
Turboprop
When the fan is replaced by a plain old propeller working at a much slower rotational speed, the use of a speed reduction gearbox with a larger ratio is a required all the more for the same reasons.
The Dash 8 / Q400 which has STOL performances, is equipped with two PW150A turboprops. The PW150A is a two-spool core with a free power turbine (two discs not linked to the gas generation section). The free turbine allows for better propeller speed management, allowing an engine start with the propeller stopped.

From its EASA certificate, the HP shaft runs at 31,150 RPM, the LP shaft at 27,000 and the maximum output shaft speed doesn't exceed 1,020 RPM.

PW150A (source)
Note: this schematic is not accurate, but it illustrates the principle. Look with an accurate (but less readable) schematic of the engine sections.

Additional experimentation: Propfan
Interestingly there is an intermediate solution between the fan and the propeller: The unducted fan. It combines the advantages of a high rotational speed and the lack of duct, the drawback being the noise generated by unducted blades close to Mach 1 airflow at the tip.
Testing was conducted by several engine manufacturers but no engine was launched on the commercial market for reasons that appear to be non-technical. An example studied by GE and Nasa combined a double unducted fan (UDF) and a free turbine in a new type of engine known as propfan, in a pusher configuration.

(Source)
The two counter-rotating fans were mounted directly on the free turbine output shaft without a gearbox.

You are right, it is desirable to avoid the gearbox. Big turboprop engines use a two-spool design in which the low pressure turbine is exclusively turning the propeller. However, this also needs a gearbox, albeit with a smaller gearing ratio. The gearbox has been accepted by engine designers as the lesser of two evils, the bigger evil being an excessively large turbine.

Cut-away drawing of the AE-2100 turboprop engine (picture source). The turbine has four stages, the first two driving the high-speed spool and the 14-stage compressor, while the inner, low-speed spool is driven by the last two turbine stages and is connected to the gearbox in front.
If the turbine would spin slowly enough to avoid a gearbox altogether, it would need to be much bigger. This would result in an undesirably large nacelle, causing an equally undesirable drag increase. Also, the larger, slower-spinning turbine will make the whole engine much heavier, not simply because the turbine wheel is larger, but mostly because the engine casing has to become much larger, too. Note in the cut-away picture of the AE-2100 above that the low speed turbine is already the widest component - making it any wider would increase drag and engine mass significantly.
The rotational speed of the turbine easily doubles or triples the flow speed at the turbine blade, thus increasing the dynamic pressure at the blade by a factor between four and nine over the dynamic pressure of the axial flow at the exit area of the high speed turbine. A slower turbine would work at a much lower dynamic pressure and will need an increased radius to still give the same torque, which is the product of blade lift and radius. Only the increased number of blades and the increased radius of a much bigger turbine will compensate for the much lower dynamic pressure at the turbine blades.

I imagine to turn huge propeller you need a lot of torque. Gearbox multiples the torque. The engine I know reduction is 16:1 so 16 times multiplication. If you don't use gearbox you will need turbine to be the size of the propeller! I don't see any easy way to increase torque generated by turbine. Current turbo props use several turbine discs already so you will need to add 30!!! discs but that will be more complex, expensive and heavy then the gearbox. Also you will need a very strong and big shaft not to mention if it will be aerodynamically effective solution!!!


text:
Do aircraft need special modifications for polar routes?
Does an aircraft need special modification for polar routes?

There are several considerations for flying polar routes, but no special modifications are necessarily needed.  Navigation is different, as Lat/Lon (specifically longitude) converge to become meaningless close to poles, so aircraft traditionally use a grid navigation system.  Aircrew should also be aware of the difference between magnetic and true north, as the magnetic "North Pole" is different than the geographical North Pole.
You should also understand your aircraft's temperature boundaries.  If you fly through the arctic in the depth of winter, you should ensure that all of your aircraft components are suitable for the temperature.  Usually, this isn't an issue - and if it was, you can always descend a bit to find "warmer" air.
Otherwise, air provides lift in the polar regions just like in the equatorial regions, and Bernoulli keeps your aircraft afloat!

Those navigation troubles were very real in the pre-GPS days. Today, almost no pilot anywhere relies exclusively on the magnetic compass, and celestial navigation is also a thing of the past...

HF radios and ETOPS certification are also needed.

I read of one light aircraft that flew directly over the NPOLE waypoint and his GPS crashed because its software apparently couldn't handle the longitude issue there.


text:
How many flights can be made under EASA permit to fly?
I understand the permit to fly is valid for 14 days, but how many flights can be made in that time?

I went to look at a PtF I got for one of my projects, and we had no limits, neither in time nor in amount of flights, so I am not sure that we can answer your question without seeing a copy of your PtF.

Assuming you mean a temporary Permit to Fly (rather than a 'permanent' one) for an aircraft normally flying under a C of A, then this site states that:

You will be required

to supply a validity period while completing the application.
Temporary permits are usually issued for less than a month, but you should allow enough time for the flight to be conducted, taking into account weather conditions etc.

I'd guess it is intended for an aircraft to be ferried in order to renew its C of A or at the end of its operational life?


text:
Is it practical to use wires to stiffen rotor arms?
(Related to my last question on ducting.)
Wires have been used in the past to stabilize wings with a very low weight cost. Could something similar be use to stabilize the arms for a UAV's rotors?
Assuming I don't have enough money to build a custom 8 arm (based on previous advice) carbon fiber frame, could the wiring approach be applied to UAVs? I ask because for a V1 prototype PVC is cheap and relatively strong, but I could enhance it with a bit of aluminum plate in the center and small aircraft cable in tension.

What kind of wire are you thinking of using?

I was thinking 1/16 aircraft cable top and bottom to put the arm in tension. Could also go with nylon to save weight but I would be concerned about it stretching and ultimately failing.

I mean, I see little reason why not. The only issue I could see appearing is that the wire on top might intersect the prop circle.

I thought of that too. Obviously I'll have to keep that from happening. It'll probably only go about halfway out the arm, but it will still reduce the flex of the arm significantly. Thanks.

And ifconfig if you post your comment as an answer I'll accept it. Like the name btw.

I see little reason why small gauge wire couldn't be used to strengthen rotor arms on a multirotor. The only major issue I could see developing is that the wire on the top side of the arm might accidentally intersect the prop circle.
MS Paint sketch of a possible design idea:

This would stiffen the arm, sure.  Even kevlar thread or piano wire ("servo rods").  For more ideas, see https://en.wikipedia.org/wiki/Standing_rigging.


text:
Is it possible for one runway to have a different TORA in each direction?
Is it possible that TORA is not the same for both directions on a single runway?

Do you mean one the same runway in opposite directions?

yes, same runway in opposite direction.

Yes.  If you look at the information for London Gatwick as an example, 08R has a TORA of 3159 meters, whereas 26L has a TORA of 3255 meters.
http://www.ead.eurocontrol.int/eadbasic/pamslight-7B4054FA19E6240FA6A62C9356F52804/7FE5QZZF3FXUS/EN/AIP/AD/EG_AD_2_EGKK_en_2018-12-06.pdf

How about runway length for both runways?

The strip of grass or tarmac will be the same length from whichever end you measure it.  However, there are a host of factors that affect the runway available for takeoff and landing.  You can see some other measures in the linked document headed TODA (take off distance available), ASDA (accelerate stop distance available) and LDA (landing distance available).  If you want more information on how any of those are calculated, you should ask a new question :)


text:
In what situation could the maximum ramp mass limit the allowed take off mass?
I’ve been pondering this for the longest time, but have been unable to come to a conclusion.

If I understand your question correctly, then at an airport where the expected taxi-out fuel burn is larger than the difference between maximum ramp and maximum takeoff mass, the mass at start of takeoff would always be restricted by the maximum ramp mass (if not by other factors like performance).

I don't really understand your question, but does this one answer you?

@Pondlife: I guess the OP is asking if the limit on the MRM could, in particular conditions, or for a particular aircraft, be so low that it would prevent the MTOM to be reached. But some clarification in the post would be good.

@vasin is correct. I'll put some actual numbers in a scenario.
A 747-481F has a max ramp weight of 913000lb, a MTOW of 910000. That 3000lb difference between max ramp and MTOW has been the same for 747s since the -100 airplanes.
The 3000lb is usually sufficient to cover the taxi fuel, but not always. Think having to taxi out at JFK when departures are heavy and the runway in use is the one farthest away from your ramp. Or, same thing at Honolulu and because of your weight you need the reef runway.
The dispatcher/load planner for the flight believes in following the rules, and he believes the taxi out will consume 4000lb. Thus, he has to use 909,000 as the max takeoff weight. Thus the max ramp mass has limited the MTOW
This kind of thing happens most on freighter flights because they're loaded as often as possible right up to their max zero fuel weight, that's where the money is. So let's say it's a freighter flight, JFK to Tokyo Narita. With the airplane near MZFW, you can't load enough fuel to get to Tokyo, but if you stretch a string on a globe between JFK and Narita, it goes almost right over Anchorage, and Anchorage is pretty much at the halfway point. Indeed, Anchorage has been used as the refueling stop for freighters for years and for pax aircraft as well, but especially for freighters.
Anyway, the load planner will put as much cargo aboard as possible to put the actual takeoff weight right up against the MTOW allowed.

**assume the allowed takeoff mass means MTOW.
MTOW means the maximum weight at which the pilot is allowed to attempt to take off, due to structural or other limits.
This includes all mass involves in the flight including MZFW, fuel and consumables. Both maximum ramp mass and MTOW are a fixed number regardless of temperature or airport altitude. since maximum ramp mass and MTOW are fixed number, if fuel burn during taxi out is greater than the difference between maximum ramp mass and MTOW, maximum ramp mass will limit maximum weight an aircraft can takeoff with.


text:
How do I do these VOR time and distance calculations?
I'm trying to figure out the calculation to these questions:

A pilot tracking a VOR turns 90 degrees from current heading. The
  pilot notes that it takes 3.0 minutes for the plane to intercept the
  radial 5 degrees from where it previously was. What is the time to
  VOR?

And:

Using the previous question, what is the aircraft speed if the
  distance to travel is 100 miles?

I used the formulas my professor gave me and the numbers are coming out unrealistic to me. Could someone walk me through how to get the correct answer?


text:
How can I calculate the angle of attack of an airfoil?
Can someone provide me a general algorithm to compute the angle of attack of an airfoil, and some theory along with it?

What are your "knowns"?  For example, they could be a) a sketch showing the shape of the airfoil and the direction of the free-stream relative wind, or b) the angle of the wing's mean chord line relative to the ground, the aircraft's horizontal speed, and the aircraft's vertical speed.  Two totally different problems, but each of which could allow you to compute the angle-of-attack of the wing.  So can you tell us a little more about what you are trying to do, what "knowns" you are starting with?

Other versions of the problem could involve a known angle-of-attack at one airspeed, and desire to know the a-o-a at a new airspeed, where the slope of the lift-coefficient -versus- a-o-a curve is known.  So... the question as you've asked it seems a bit too open-ended.

The angle of attack is the angle between the wing and the direction of flight. The direction of flight is opposite to the airflow, so the angle of attack is also the angle between the wing and the relative wind.
For a more refined definition (thanks @Peter Kämpf): The flight path direction (the velocity vector in the language of aerodynamicists) should be expressed relative to the air mass, not to the ground (as measured by an inertial system), but that's beyond the topic.

How to compute it? Well, it's like airspeed, we don't. It's just measured using a small windvane:

A380 angle of attack sensor (combined with a Pitot-static), source
In the image above, the black angle of attack sensor is combined with a classic Pitot-static which measures airspeed. On airliners, there are usually several AOA sensors. The one in the picture is located on the FO side, air comes from the right side.
Another simple AOA sensor at the bottom, Captain side:

Source (original source not found)
There is a specific AOA sensor found on GA aircraft, to trigger an alarm when approaching the critical angle of attack: The stall sensor:

Source
This strip located at the wing leading edge has two positions and rock abruptly before the critical angle of attack is reached. It triggers an alarm in the cockpit, so that the pilot can reduce the angle of attack.

A final note: The AOA wasn't displayed to the crew in the cockpit, only the pitch angle was. Newer aircraft now display both. I think it was a recommendation of the BEA after AF447 accident, were the crew couldn't figure out the AOA they were at after a Pitot-static froze.

Minor nitpick: The definition is only correct for zero wind.

@PeterKämpf: I added the caveat, thanks!

First and foremost, we need to define what Angle of Attack is.
The angle of attack in fluid dynamics is the angle between a reference line on a body and a vector which represents the flow of fluid over the body.
For aircraft, we are generally talking about the wing's angle of attack to produce lift. To do this we substitute a chord line for the body, and the wind direction for the vector. However, the AOA is constantly changing during flight, because of this the most common way of finding your angle of attack is to measure it. In-flight this is done by using an Angle of Attack indicator shown below

]2
The method used to measure the angle of attack is described in this article

The AOA tube is constructed with two tiny machined holes to create differential pressure sources. One hole is bore-sighted at the front of the AOA tube along the longitudinal axis, while the second, located at the bottom of the AOA probe, is pointed downward at a 45-degree angle to act as a reference source.
From here the data is sent to a computer which determines the current AOA and adjusts the indicator appropriately.

AOA can also be roughly determined in-flight by taking the difference of the aircraft's angle of incidence and flight-path vector; however in rough weather and turbulence this method becomes inaccurate.
For computation purposes, the AOA is calculated by taking the absolute value of the result you get from the difference between the direction of wind and direction of the chord of the wing:

AOA = |wind-chord|

With that said, if you are going to try to convert this into a coefficient of lift, it's important to remember that the lift of a finite wing at a certain AOA is less than the lift of an infinite wing at the same AOA. For that, I will leave you this link which may be helpful.

AOA is taken by gathering the arctangent of (w / u)
or arctangent (v_z / v_x)
Where w (or v_z) is the speed (velocity) of motion downwards (relative to the body) where up is positive [and of course, down is negative] and u (or v_x) is the speed (velocity) of motion forwards and backwards where BACKWARDS IS POSITIVE [and forwards is negative]
The only problem I have with this method of calculation is that your AOA only goes upto + or - 90 degrees before 'doubling back' and inversing your upright state (e.g. going upside down) will STILL leave you at a positive AOA.  Not sure how to measure this, but hopefully this is a good start!
This was taken from the NASA reference here:
https://ntrs.nasa.gov/api/citations/19920002789/downloads/19920002789.pdf